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Air Pressure Testing FAQ (frequently asked questions)

• What is air leakage in buildings?
• Why is it important to build air tight dwellings?
• What is air pressure testing?
• Why do I need to test the air tightness of a building?
• When are air tightness tests carried out?
• Who is approved to carry out air pressure testing?
• What happens if a dwelling fails air pressure testing?
• How do I improve the air tightness of my house or flat?

Air leakage (also known as air permeability or air infiltration) is the air tightness of a dwelling through uncontrolled means such as cracks and gaps in the building envelope. Any ventilation system installed in a building is seen as a source of controlled air flow and is therefore not considered as air leakage. At a very basic level, air leakage may be seen as unwanted draughts.

The energy that we use to heat our homes is primarily created by burning fossil fuels that produces carbon dioxide. If we reduce the air leakage of a building we also reduce the amount of energy required to maintain comfort levels and in turn reduce carbon dioxide emissions. In 2002 the government released a White Paper with a target to reduce carbon dioxide emissions by 20% from 1990 levels by 2010. To achieve these targets, Building Regulations were revised.

Air pressure testing is a method of measuring and quantifying the air leakage of a building. In Approved Document Part L1A of the Building Regulations, Air Tightness Testing is referred to as Pressure Testing. The test methodology for measuring the air tightness of a building is set out in ATTMA Technical Standard 1. Technical Standard 1 is generally based on BS EN Standard 13829:2001, Thermal Performance of Buildings - Determination of air permeability of buildings - Fan pressurisation method. Further information is available in TM23: Testing buildings for air leakage.

Air pressure testing of a proportion of all new domestic housing is a legal requirement in accordance with the guidance given in Approved Document Part L1A - Conservation of fuel and power in new dwellings of the Building Regulations. Testing the air tightness of existing dwellings can highlight areas of problems that can be treated cost effectively to improve the energy efficiency of the dwelling as a whole.

Air tightness tests are usually carried out during the construction and commissioning process of a building when the external envelope is fully complete, with windows and external doors in place. A full list to determine the readiness of dwelling to be tested can be provided on request.

Air pressure testing may be carried out by a competent person. The British Institute of Non-Destructive Testing (BiNDT) runs a registration scheme of competent persons to ensure adherence to procedures, quality of service and UKAS calibration of equipment. Approved Document Part L1A states that a local authority is authorised to accept a certificate from a person who is registered by The British Institute of Non Destructive Testing. Air pressure testing procedures can also be accredited by UKAS.

Guidance in Approved Document Part L1A advises that failed dwelling types will require remedial work and retesting, along with one additional test on the same dwelling type. In the event of a failed air pressure test, Site Measurement Services Ltd can provide a smoke test and advice to help identify the areas of leakage and give guidance on improving the air tightness performance.